Gestational diabetes typically occurs in the second trimester of pregnancy between the 24th and 28th weeks of gestation. It’s diagnosed using a test called a glucose tolerance test, which may be either a one- or two-step process.

You can develop gestational diabetes at any point during pregnancy, but it usually develops in the second or third trimester because that’s when hormones the placenta produces, like human chorionic gonadotropin (HCG), progesterone, estrogen, human placental lactogen, and others, begin to peak.

During pregnancy, these hormones help your body produce extra glucose, providing the developing baby with additional energy. Usually, your pancreas helps manage extra glucose, but during pregnancy, it may not be able to process all the extra glucose, which can cause insulin levels to rise, leading to diabetes.

International guidelines recommend testing for gestational diabetes between 24 and 28 weeks of pregnancy. If you are at an increased risk of developing gestational diabetes, you may benefit from earlier testing; for most people, there is not enough evidence that testing early makes a difference in protecting you and your child.

The guidelines were developed because studies suggest that treating gestational diabetes around 24 weeks of gestation is associated with improved outcomes for the parent and child.

There are two main tests for gestational diabetes: The glucose challenge test and the oral glucose tolerance test (OGTT). The glucose challenge test is typically given at your 24-week prenatal appointment and screening. You do not need to fast (not eat or drink) before this test. For this test, you will be asked to drink a sweetened beverage. One hour later, your blood will be drawn, and your blood glucose level will be measured. A result of 140 or higher means you likely have gestational diabetes. If your result is 200 or more, you may have type 2 diabetes.

If you have a high result from this test, you may be asked to return for an OGTT. You will need to fast for at least 8 hours before this test. You will drink a beverage containing glucose, and then your blood will be drawn every hour for 2 to 3 hours. If two of three results are high, it means you have gestational diabetes.

Your doctor or healthcare professional will explain the results of your test and your treatment options. Treatment for gestational diabetes is essential for your health and that of your baby.

Gestational diabetes happens when your blood glucose levels are elevated during pregnancy. All pregnant people are tested for gestational diabetes around 24 weeks of pregnancy unless they are at a higher risk of developing gestational diabetes, because research suggests that, for most people, 24 weeks is an effective time to begin treating gestational diabetes.

People who are at increased risk of developing gestational diabetes may be tested earlier in pregnancy.

Speak with your doctor or healthcare professional if you have concerns about gestational diabetes.